An ERP like Workday is the IDE for an enterprise (and a safe default like VSCode & co). Any single component is always worse than an entire startup laser-focused on that problem/process (e.g., ATS), but for most business processes, "satisfying" is much better than "optimizing". When a business grows, the range of problems they need to address increases rapidly, like the surface area of a balloon being inflated. "Good enough" is good enough until it becomes so painful as to become a top problem for the CEO or the HR Head, and "which ATS we use" never crosses that threshold. Yes, getting new talent is important, but ATS friction is not a big contributor - Google/Netflix could use anything, and their pipeline would not change in either direction, so the main levers are elsewhere.
1. Cuts down on low-effort applications
2. Gives full functionality for a large company
Same reasons Google and other have their own torturous processes
First you have to find out who is really desperate to work for a company
And a lot of big companies are GREAT places to work for certain types of people
Most people, prob
And you might not even have to do an application unless and until you go to convert to full time
So you have to fill out the app, but you're already hired so it's worth it
I have never worked on this side of hiring but I would imagine if a site was so frictionless it let android engineers (for instance) do one-click apply to every company hiring android engineers that the hiring managers would have too many resumes to sort through of people who would never actually accept.